Gefion family explained

The Gefion family (FIN: 516; adj. Gefionian; also known as the Ceres family or the Minerva family) is an asteroid family located in the intermediate asteroid belt between 2.74 and 2.82 AU at inclinations of 7.4° to 10.5°. The family of S-type asteroids is named after 1272 Gefion and consists of more than 2,500 known members. It had previously been known as the Ceres family. It is still known as Minerva family, named after then thought parent body 93 Minerva, until it was identified to be an interloper into its own family.

Properties

The members have proper orbital elements in the approximate ranges^[1]

	a_p		i_p
min		0.120	8.6°
max	2.82 AU	0.148	9.6°

At the present epoch, the range of osculating orbital elements of these core members is

	a		i
min		0.081	7.4°
max	2.82 AU	0.18	10.5°

The namesake is 1272 Gefion. The family is fairly large, e.g. the Zappala 1995 analysis found about a hundred core members. A search of a recent proper element database^[2] found 766 objects (about 0.8% of the total) lying within the region defined by the first table above.

2631 Zhejiang has a diameter of 34 km, and is the largest core member whose diameter has been reliably estimated, although 2911 Miahelena is brighter, and would have a rough diameter of about 47 km, given the same (very low) albedo of 0.025.

Alternative name and interlopers

Until recently, this family was known as the Ceres family (adj. Cererean) or the Minerva family (adj. Minervian) after 1 Ceres (the largest asteroid) or 93 Minerva. However, spectroscopic analyses showed that these largest members were in fact interlopers in their own family,^[3] having a different spectral class from the bulk of the members. Other known interlopers are 255 Oppavia, 374 Burgundia, 2507 Bobone, and 2559 Svoboda.^[4] This left the fairly minor asteroid 1272 Gefion as the lowest-numbered member.

List of members

This is a list of the known family members, without the above-mentioned interlopers.

important;	Name	a (AU)	e
	2.78385	0.15170
	2.79948	0.16918
	2.79319	0.17242
	2.79898	0.16824
	2.80260	0.14050
	2.78440	0.11071
	2.79433	0.17339
	2.81456	0.15728
	2.78777	0.17198
	2.79475	0.08893
	2.78595	0.14340
	2.79730	0.16070
	2.79969	0.17422
	2.79792	0.09969
	2.80233	0.09847
	2.79520	0.09303
	2.78884	0.16849
	2.76293	0.16535
	2.79307	0.10127
	2.80586	0.15548
	2.79442	0.13349
	2.75822	0.16608
	2.77626	0.15885
	2.80989	0.15066
	2.79806	0.13498
	2.79387	0.09181
	2.78979	0.10861
	2.79463	0.15238

important;	Name	a (AU)	e
	2.80083	0.17319
	2.79967	0.09267
	2.77496	0.16644
	2.77638	0.16166
	2.80234	0.09628
	2.77489	0.15517
	2.80392	0.17351
	2.75642	0.09601
	2.78152	0.15916
	2.78088	0.16534
	2.79870	0.16302
	2.78220	0.09822
	2.78255	0.16568
	2.81240	0.16818
	2.78349	0.10158
	2.78245	0.14156
	2.75694	0.16628
	2.78591	0.09965
	2.78016	0.14078
	2.77253	0.16753
	2.76992	0.15337
	2.78176	0.15170
	2.78098	0.17028
	2.79053	0.11959
	2.76784	0.14054
	2.78004	0.09434
	2.79360	0.15011
	2.81578	0.12154

important;	Name	a (AU)	e
	2.79851	0.15765
	2.76315	0.15291
	2.76990	0.09282
	2.81210	0.10526
	2.76810	0.16222
	2.76575	0.17269
	2.81525	0.15026
	2.78514	0.15738
	2.78785	0.17691
	2.78987	0.17546
	2.77468	0.17725
	2.75828	0.11401
	2.76196	0.10315
	2.81391	0.17207
	2.80445	0.18117
	2.76196	0.14457
	2.78649	0.11048
	2.79852	0.15112
	2.76377	0.14769
	2.77225	0.10578
	2.75702	0.12711
	2.76469	0.16515
	2.74368	0.08177
	2.77635	0.10965
	2.76154	0.11756
	2.79337	0.16135
	2.78491	0.17877
	2.8035	0.1627

Notes and References

according to the HCM analysis by V. Zappalà, Ph. Bendjoya, A. Cellino, P. Farinella and C. Froeschlé, Asteroid Families: Search of a 12,487-Asteroid Sample Using Two Different Clustering Techniques, Icarus, Volume 116, Issue 2 (August 1995), pages 291–314
https://newton.spacedys.com/cgi-bin/astdys/astibo?proper_elements:0;main AstDys
A. Cellino et al. Spectroscopic Properties of Asteroid Families, in Asteroids III, p. 633-643, University of Arizona Press (2002). (Table on page 636, in particular).
Identified by inspection of the SMASSII data set, S.J. Bus and R.P. Binzel, Phase II of the Small Main-Belt Asteroid Spectroscopic Survey, Icarus Vol. 158, p. 106 (2002).